//base64转blob
function dataURLtoBlob(dataurl) { 
	var arr = dataurl.split(','),
		mime = arr[0].match(/:(.*?);/)[1],
		bstr = atob(arr[1]),
		n = bstr.length,
		u8arr = new Uint8Array(n);
	while (n--) {
		u8arr[n] = bstr.charCodeAt(n);
	}
	return new Blob([u8arr], { type: mime });
}


//将blob转换为file
function blobToFile(theBlob, fileName){
   var file = new File([theBlob], fileName, {type: theBlob.type, lastModified: Date.now()});
   return file;
}